I can send a screen-shot of the setting in my system as a new user I am not allowed to attach the image in this query.I have tried logging out as well as restart of my system. Request someone to help on this.

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Goto: System Configurations -> Keyboard -> shortcuts -> Navigation. And there you will see Hide all normal windows. If it is Disabled click on it and press <kbd>Ctrl</kbd>+<kbd>Alt</kbd><kbd>D</kbd>. It works?
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LucioSep 5 '12 at 18:59